The present invention relates to the art of image reconstruction. It finds particular application in conjunction with CT scanners and will be described with particular reference thereto. However, it is to be appreciated that the present invention is also applicable to the reconstruction of images from magnetic resonance data, digital x-ray data, PET data, and the like.
A CT scanner generates lines or views of image data values. The data values of each view commonly represent radiation attenuation along rays of a fan shaped swatch through a slice of a patient. Different views represent the same fan shaped swatch but at different angular orientations about the patient. The views of data are collected in a data memory and reconstructed into an image representation, most commonly by a process of convolution and backprojection, also known as filtered backprojection. By filtering all the views with a common filter, image artifacts, noise degradation, and the like can be reduced or eliminated. Conventionally, all views are filtered with the same filter function.
In U.S. Pat. No. 4,333,145, only some data is filtered prior to the reconstruction. The data collected from rays which pass through the patient's arm pass through more bone than other rays giving that data a different bandwidth. The '145 patent filters only the rays of data that pass through the patient's arms with a preselected fixed filter function to reduce or eliminate bandwidth related artifacts in the resultant image.
Data from other scanners has also been filtered either as the data is collected or reconstructed into an image representation. However, such filtering again tends to be fixed for a given image.
The present invention contemplates a new and improved filtering technique which overcomes the above referenced problems and others.